Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Enhancing food security through a multi-stakeholder process: the global agenda for sustainable livestock
Breeman, G.E. ; Dijkman, J. ; Termeer, C.J.A.M. - \ 2015
Food Security 7 (2015)2. - ISSN 1876-4517 - p. 425 - 435.
governance - chains - policy
Feeding the world is not only a complex technical matter, but also a demanding governance issue. As food security has all the characteristics of a wicked problem (variety of problem definitions, conflicting interests, interconnectedness across scales, inherent uncertainties), conventional governance arrangements do not seem to work. New ways of concerted actions are introduced to better link global challenges with local practices. One example of this is the Global Agenda for Sustainable Livestock: a partnership of public, private, social, and civil society actors, committed to the sustainable development of the livestock sector. It aims to enhance shared understanding of sustainability and its underlying development issues and to build consensus on the path towards sustainable food security through dialogue, consultation, and joint analyses. This article analyses the Agenda as a new type of governance arrangement to enhance food security. It relies on a theoretical framework that consists of five governance capabilities, which are considered crucial for coping with wicked problems: reflexivity, resilience, responsiveness, revitalisation, and rescaling. The aim of this paper is threefold: 1) to assess the Agenda and learn from that; 2) to evaluate the capabilities framework as a tool to assess governance arrangements; and 3) to reflect on the potentials of new governance arrangements to deal with food security. The article illustrates how the governance capabilities framework can be used as a tool to analyse the multi-stakeholder platform for enhancing food security. It concludes that the Agenda successfully encompasses many elements of these capabilities although improvements are possible.
Sustainability assessment of salmonid feed using energy, classical exergy and eco-exergy analysis
Draganovic, V. ; Jorgensen, S.E. ; Boom, R.M. ; Jonkers, J. ; Goot, A.J. van der - \ 2013
Ecological Indicators 34 (2013). - ISSN 1470-160X - p. 277 - 289.
krill euphausia-superba - life-cycle assessment - environmental impacts - production systems - farmed salmon - ethanol - organisms - products - chains - wheat
Reduction of the environmental impact of feed products is of paramount importance for salmon farming. This article explores the potential to compare three thermodynamically based ecological indicators. The environmental impact of partial replacement of fish meal (FM) and fish oil with alternative ingredients was investigated using energy, classical exergy and eco-exergy analysis. Seven hypothetical feeds were formulated: one with high levels of FM and fish oil, four feeds based on plant ingredients, one containing krill meal, and one based on algae-derived products. Analysis included cultivation of crops and algae, fishing for fish and krill, industrial processing of these ingredients and production of complete fish feed. Because most harvested products are refined in multiple product outputs that have good value to society, two scenarios were compared. In the base case scenario, no allocation of co-products was used and all the environmental costs were ascribed to one specific co-product. Co-product allocation by mass was used in the second scenario; this is considered to be the preferred scenario because it accurately reflects the individual contributions of the co-products to the environmental impact of the feed products. For this scenario, the total energy consumption for a fish-based diet was 14,500 MJ, which was similar to a krill diet (15,600 MJ), about 15–31% higher than plant-based diets, and 9% higher than an algae diet. Substituting FM and fish oil with alternative ingredients resulted in minor changes in total classical exergy degradation (2–16% difference). The calculations based on energy only consider the energy conservation based on the First Law of Thermodynamics, whereas those based on classical exergy also takes the Second Law of Thermodynamics into account; energy that can do work is distinguished from energy that is lost as heat to the environment. The calculations based on eco-exergy consider the total loss of work energy in the environment including the work energy associated with the information embodied in the genomes of organisms. The diet based on fishery-derived ingredients was the highest total work energy consumer compared with plant-based diets (24–30% greater), the diet containing krill meal (25% greater), and the algae diet (four times higher). Thus, reducing FM and fish oil levels in fish feed can contribute significantly to more sustainable aquaculture. In particular, algae-derived products in aquafeeds could drastically decrease environmental costs in the future.
Vegetable production in the Red River Delta of Vietnam. I. Opportunities and constraints
Huong, P.T.M. ; Everaarts, A.P. ; Neeteson, J.J. ; Struik, P.C. - \ 2013
NJAS Wageningen Journal of Life Sciences 67 (2013). - ISSN 1573-5214 - p. 27 - 36.
lowland - system - hanoi - management - chains - asia
An overview is given of the natural, socio-economic, agronomical and marketing conditions for vegetable production in the Red River Delta (RRD) of Vietnam. The seasonal variation in temperature in the RRD is the main determinant for the production season of vegetables. Heavy rainfall in the hot season increases production risks, as it may physically damage crops. Frequent rainfall in this period may enhance disease incidence. Landholdings are small and individual plots are the smallest of Indochina. Vegetables typically are produced in flooded rice based systems. Such systems are characterized by poor soil structure for vegetable production and high labour demand for the construction of raised beds. Highly perishable crops can only be grown close to the markets in the peri-urban areas. Less perishable crops can be produced further away from the city markets. Generally, large quantities of pesticides are used and there is increasing public concern about pesticide residues on products. The small landholdings, small plots and consequently the small amounts of product, limit effective marketing and make the producers dependent on collectors. Given the trends in population dynamics and human diets, urban vegetable demand in the RRD, however, has ample opportunities to grow. Effects have been analysed and categorised in opportunities and constraints for adopting improvements. A potential pathway to sustainable development is the development of permanent vegetable production systems, with producers co-operating in producers organizations, enabling them to work on a larger scale, produce larger volumes, introduce harvest date planning and quality control and aim for the integration of production with marketing in a vegetable value chain. By simultaneously adopting Good Agricultural Practices, consumers’ food safety concerns can be addressed. The expected increase in vegetable demand is likely to open new opportunities for the RRD vegetable producers
The ‘devils triangle’ of MSC certification: Balancing credibility, accessibility and continuous improvement
Bush, S.R. ; Toonen, H.M. ; Oosterveer, P.J.M. ; Mol, A.P.J. - \ 2013
Marine Policy 37 (2013). - ISSN 0308-597X - p. 288 - 293.
seafood - conservation - fisheries - chains - system
The Marine Stewardship Council (MSC) has continued to strengthen its position in the market based on its credibility as a transparent, accountable and science-based third party certification scheme. However, the consolidation of MSC's credibility risks being undermined by the poor representation of developing world fisheries and concerns that the scheme provides little incentive for continual improvement for fisheries once certified. This paper argues that the challenge of maintaining credibility while increasing access and fisheries improvement constitutes a ‘devils triangle’. In the absence of a clear policy from MSC for balancing this triangle fisheries are taking their own actions to differentiate themselves both above (MSC-plus) and below (MSC-minus) the certification threshold. To avoid further undermining of the MSC the organisation should internalise such externally-led differentiation by moving towards an internally controlled tiered certification system based on its already existing metric-based principle indicator system. Doing so would communicate on equity and continual improvement both before and after certification, and create on-going incentives for fishers to enter into the MSC programme.
Direct measurement of the strength of single ionic bonds between hydrated charges
Spruijt, E. ; Berg, S.A. van den; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2012
ACS Nano 6 (2012)6. - ISSN 1936-0851 - p. 5297 - 5303.
molecule force spectroscopy - microscopy - afm - proteins - dna - complexes - chromatin - brushes - chains
The strength of ionic bonds is essentially unknown, despite their widespread occurrence in natural and man-made assemblies. Here, we use single-molecule force spectroscopy to measure their strength directly. We disrupt a complex between two oppositely charged polyelectrolyte chains and find two modes of rupture: one ionic bond at a time, or cooperative rupture of many bonds at once. For both modes, disruption of the ionic bonds can be described quantitatively as an activated process. The height of the energy barrier is not only lowered by added salt, but also by the applied force. We extract unperturbed ionic bond lifetimes that range from milliseconds for single ionic bonds at high salt concentration to tens of years for small complexes of five ionic bonds at low salt concentration.
Fluorescence of Alexa Fluor dye tracks protein folding
Lindhoud, S. ; Westphal, A.H. ; Borst, J.W. ; Visser, A.J.W.G. ; Mierlo, C.P.M. van - \ 2012
PLoS ONE 7 (2012)10. - ISSN 1932-6203 - 8 p.
azotobacter-vinelandii apoflavodoxin - resonance energy-transfer - beta parallel protein - molten-globule state - flavodoxin-ii - molecules - pathway - chains - intermediate - spectroscopy
Fluorescence spectroscopy is an important tool for the characterization of protein folding. Often, a protein is labeled with appropriate fluorescent donor and acceptor probes and folding-induced changes in Förster Resonance Energy Transfer (FRET) are monitored. However, conformational changes of the protein potentially affect fluorescence properties of both probes, thereby profoundly complicating interpretation of FRET data. In this study, we assess the effects protein folding has on fluorescence properties of Alexa Fluor 488 (A488), which is commonly used as FRET donor. Here, A488 is covalently attached to Cys69 of apoflavodoxin from Azotobacter vinelandii. Although coupling of A488 slightly destabilizes apoflavodoxin, the three-state folding of this protein, which involves a molten globule intermediate, is unaffected. Upon folding of apoflavodoxin, fluorescence emission intensity of A488 changes significantly. To illuminate the molecular sources of this alteration, we applied steady state and time-resolved fluorescence techniques. The results obtained show that tryptophans cause folding-induced changes in quenching of Alexa dye. Compared to unfolded protein, static quenching of A488 is increased in the molten globule. Upon populating the native state both static and dynamic quenching of A488 decrease considerably. We show that fluorescence quenching of Alexa Fluor dyes is a sensitive reporter of conformational changes during protein folding.
Variation in implementation of corporate social responsibility practices in emerging economies' firms: A survey of Chilean fruit exporters
Klerkx, L.W.A. ; Villalobos, P. ; Engler, A. - \ 2012
Natural Resources Forum 36 (2012)2. - ISSN 0165-0203 - p. 88 - 100.
critical perspectives - private standards - chains - csr - globalization - initiatives - management - countries - contract - safety
As in many sectors in emerging economies, the concept of corporate social responsibility (CSR) has become important for exporting agri-food firms in view of their integration in global supply chains. The purpose of this research was to assess the implementation by Chilean fruit exporters of CSR practices that go beyond minimum legal requirements. The principal results are that, although socio-economic components of CSR such as poverty reduction and socially just working conditions receive much attention, firms consider comprehensive environmental practices as less important. The results also indicate a slightly higher implementation of comprehensive CSR practices by large firms as compared to small and medium sized enterprises (SMEs). The main conclusion is that, although CSR is increasingly considered by Chilean firms, among SMEs in particular, more attention needs to be paid to raising awareness among managers about CSR practices and to providing assistance in their implementation. This supports findings on CSR implementation in other emerging economies that an active role of civil society and industry organizations is key and that targeted support strategies are needed to install a holistic awareness of CSR and help firms to improve on those aspects of CSR that are relatively underdeveloped.
Dendritic versus linear polymer brushes: Self-consistent field modeling, scaling theory, and experiments
Polotsky, A.A. ; Gilich, T. ; Borisov, O.V. ; Leermakers, F.A.M. ; Textor, M. ; Birshtein, T.M. - \ 2010
Macromolecules 43 (2010)22. - ISSN 0024-9297 - p. 9555 - 9566.
neurofilament brush - ionic-strength - monte-carlo - chains - macromolecules - stabilization - conformation - simulation - surfaces - collapse
Equilibrium structural properties of polymer brushes formed by dendritic polymer chains (dendrons) are studied by means of Scheutjens-Fleer self-consistent field (SF-SCF) modeling and scaling analysis. Limiting cases of minimal and maximal possible losses of conformational entropy corresponding to different assumptions concerning distribution of elastic tension in the end-grafted dendrons are analyzed on the basis of the Flory-type scaling approach. The numerical SCF modeling indicates that the effective exponent of the power-law dependence for the height of dendritic brush on the grafting density differs from that derived within the Flory-type approximation. This is explained by changing of the intramolecular elastic tension distribution upon an increase in grafting density. The distributions of end and branching points are wide and exhibit multiple maxima, pointing to a broad distribution in the chain stretching. This distribution leads to monotonically decreasing overall density profiles. The theoretical results are in line with experimental findings on linear and dendritic poly(ethylene glycol) layers end-grafted onto TiO2 surfaces
Transformations of Vietnamese shrimp aquaculture policy: empirical evidence from the Mekong Delta
Tran Thi Thu Ha, Ha ; Bush, S.R. - \ 2010
Environment and Planning C. Government and Policy 28 (2010). - ISSN 0263-774X - p. 1101 - 1119.
global agrifood system - environmental governance - fair trade - certification - thailand - impacts - chains - space
International environmental and social concerns about tropical shrimp production have led to the emergence of private transnational governance and regulation. Using cases from Ca Mau we investigate how the shift to private transnational regulatory networks has changed the role of the government from a regulator to a facilitator of global private governance interests and arrangements. The rise of these various schemes has also been part of a shift from quantitative to qualitative policy goals within the Vietnamese aquaculture sector. In turn, this has led to new internal relationships, most notably the repositioning of private interests and community-based management within the Vietnamese state framework. We conclude that the ongoing transformation of the government’s role in environmental shrimp governance requires mechanisms that foster improved participation and compliance between the state and private actors. To achieve this efforts are needed to better include local government at both communal and village levels and to use existing global market incentives more strategically.
Towards a cross-cultural typologgy of trust in B2B food trade
Hofstede, G.J. ; Fritz, M. ; Canavari, M. ; Oosterkamp, E.B. ; Sprundel, G.J.F.T. van - \ 2010
British Food Journal 112 (2010)7. - ISSN 0007-070X - p. 671 - 687.
networks - industry - agriculture - chains
Purpose – This paper aims to develop a hierarchical typology of trust elements for business-to-business trade among European companies in the food sector. Design/methodology/approach – The paper integrates desk research literature study and a qualitative survey of food industry companies. An extensive literature review about inter-organizational trust lays a foundation for designing a draft typology based on previous studies, with special attention paid to the influence of culture. Fine-tuning and validation of the typology is achieved through an exploratory field study based on 18 qualitative in-depth interviews with key informants in five EU countries, involving practitioners from the fresh fruit and vegetable, grain, meat and olive supply chains. Findings – A detailed typology of trust is developed. Although it is highly specific to the food industry, it is designed to be neutral to culture and sector, thus allowing the identification of differences in culture when dealing with trust building elements in different sectors in the food supply chain. Research limitations/implications – Since the buyer's perspective is adopted in this paper, further research is needed to validate the typology on the seller side. The typology developed here must also be tested in practice, for instance within a descriptive research quantitative study, aimed at quantifying the relative importance of the different trust elements. Practical implications – The typology stimulates the consideration of cross-cultural or cross-sector differences in the salience of trust attributes and its construction process confirms that reputation management is an extremely important determinant of success or failure. It can serve as a checklist for any company that is interested in improving its relationships with suppliers or buyers. Originality/value – The paper adds to the body of knowledge about inter-organizational trust, providing researchers with a useful tool for conducting experimental research on trust creation mechanisms
Experts' perspectives on the implementation of traceability in Europe
Kher, S.V. ; Frewer, L.J. ; Jonge, J. de; Wentholt, M.T.A. ; Howell Davies, O. ; Luijckx, N.L. ; Cnossen, H.J. - \ 2010
British Food Journal 112 (2010)3. - ISSN 0007-070X - p. 261 - 274.
food safety - consumer perceptions - delphi - quality - issues - chains
The research presented in this paper aims at understanding the views of European food risk management experts on food traceability implementation, implementation of the general food law, and the advantages the system can offer for effective risk mitigation
Organizing information integration in agri-food: A method based on a service-oriented architecture and living lab approach
Wolfert, J. ; Verdouw, C.N. ; Verloop, C.M. ; Beulens, A.J.M. - \ 2010
Computers and Electronics in Agriculture 70 (2010)2. - ISSN 0168-1699 - p. 389 - 405.
enterprise - management - technology - framework - science - chains - cimosa - eai
Agri-food enterprises operate in a complex and dynamic environment. To meet increasing demands of consumers, government and business partners, enterprises continuously have to work on innovations of products, processes and ways of cooperation in agri-food supply chain networks (AFSCN). Hence, a development towards a more knowledge-based economy is needed. The Lisbon strategy, launched by the European Union, to attain this knowledge-based economy, has failed so far. This paper argues that information sharing and organizing ICT are main critical areas to overcome this deadlock. However, ICT development in AFSCN involves an information integration task that has to deal with technical and organizational requirements and starts with an existing installed base. Traditional software engineering approaches are inadequate to address these issues. This paper provides an overall method for analysis, design and implementation of information integration, taking technical as well as organizational development into account. The method was derived from experiences in a research and development program in the Dutch arable farming sector. A generic integration framework forms the backbone of the method to ensure systematic and sustainable ICT development. Business process management (BPM), in combination with reference information models, plays an important role. The technical architecture and infrastructure are based on a service-oriented architecture (SOA). Attention is paid to the organizational infrastructure that is needed to embed the results in the right context, so that they will be broadly supported and used. The method is divided into three phases: analysis, basic design and iterative implementation. Analysis of the current situation in AFSCN is supported by an information integration framework. The basic design is a first version of the generic integration framework. In the iterative implementation phase, pilot projects are guided by this basic design, which results in incremental growth of the framework. The pilot projects follow a Living Lab (LL) approach. LLs represent a user-centric, open innovation approach for sensing, prototyping, validating and refining complex solutions in multiple and evolving real life contexts. The method is illustrated by an application to the Dutch arable farming sector. It can be concluded that the contribution of the presented method lies in combining different methodologies into a design approach for information integration, based on a sound architecture. The presented method leads to ICT that follows the business processes in real life and thus enhances appropriate information sharing to support a knowledge-based economy
Mechanical unfolding of a homopolymer globule studied by self-consistent field modeling
Polotsky, A.A. ; Charlaganov, M. ; Leermakers, F.A.M. ; Daoud, M. ; Borisov, O.V. ; Birshtein, T.M. - \ 2009
Macromolecules 42 (2009)14. - ISSN 0024-9297 - p. 5360 - 5371.
microphase coexistence - polymeric brushes - poor solvents - afm - deformation - transitions - molecules - chains
We present results of numerical self-consistent field (SCF) calculations for the equilibrium mechanical unfolding of a globule formed by a single flexible polymer chain collapsed in a poor solvent. In accordance with earlier scaling theory and stochastic dynamics simulations findings we have identified three regimes of extensional deformation: (i) a linear response regime characterized by a weakly elongated (ellipsoidal) shape of the globule at small deformations, (ii) a tadpole structure with a globular "head" coexisting with a stretched "tail" at intermediate ranges of deformations, and (iii) an uniformly stretched chain at strong extensions. The conformational transition from the tadpole to the stretched chain is accompanied by an abrupt unfolding of the depleted globular head and a corresponding jump-wise drop in the intrachain tension. The unfolding-refolding cycle demonstrates a hysteresis loop in the vicinity of the transition point. These three regimes of deformation, as well as the first-order like transition between the tadpole and the stretched chain conformations, can be experimentally observable provided that the number of monomer units in the chain is large and/or the solvent quality is sufficiently poor. For short chains, on the other hand, under moderately poor solvent strength conditions, the unfolding transition is continuous. Upon an increase in the imposed end-to-end distance the extended globule retains a longitudinally uniform shape at any degree of deformation. In all cases the system exhibits a negative extensional modulus in the intermediate range of deformations. We anticipate that predicted patterns in force-deformation curves for polymer molecules in poor solvent can be observed in single molecule atomic spectroscopy experiments.
Interaction of particles with a polydisperse brush: A self-consistent-field analysis
Vos, W.M. de; Leermakers, F.A.M. ; Keizer, A. de; Kleijn, J.M. ; Cohen Stuart, M.A. - \ 2009
Macromolecules 42 (2009)15. - ISSN 0024-9297 - p. 5881 - 5891.
protein adsorption - polymer brushes - chains - layers
Two complementary theoretical approaches are used to study the effect of polydispersity oil (anti)fouling properties of a neutral polymer brush. Polydispersity is described using the Schulz-Zimm distribution. The Scheutjens-Fleer self-consistent-field (SF-SCF) formalism is used to consider the interaction between a single particle and a polydisperse brush with grafting density sigma, focusing on the influence of the polydispersity index. The larger the polydispersity, the easier it is for a small particle (with radius R similar to 1/(2 root sigma)) to penetrate the brush. Hence, the monodisperse brush is better suited to protect a surface against the adsorption of small particles compared to a corresponding polydisperse brush. The brush grafting density, however, remains the most important parameter for timing the brush antifouling properties against small particles. For large particles (modeled as a flat wall.) an opposite effect of polydispersity is found: it is harder to compress a polydisperse brush than it corresponding monodisperse brush, and thus a polydisperse brush is better suited to protect the Surface against adsorption of large particles. A less-detailed approach, based on the stacking of Alexander-de Gennes boxes, is used to study the adsorption of many particles into a polydisperse brush. Consistent with the single-particle data generated by the SF-SCF theory, for weak attraction between the particles and the brush the absolute adsorbed amount remains low but increases strongly as a function of polydispersity (from M-w/M-n = 1-2 by a factor of 2-4). Obviously, at higher attraction between the particles and the brush the adsorption increases, but a less strong dependence on the polydispersity index is observed.
Chain governance, sector policies and economic sustainability in cocoa; A comparative analysis of Ghana, Côte d'Ivoire, and Ecuador
Ton, G. ; Hagelaar, J.L.F. ; Laven, A. ; Vellema, S. - \ 2008
Wageningen : Wageningen International (Markets, chains and sustainable development 12) - ISBN 9789085854005 - 40
economische ontwikkeling - economisch beleid - overheidsbeleid - kettingen - cacao - economische analyse - ghana - ivoorkust - ecuador - duurzame ontwikkeling - economic development - economic policy - government policy - chains - cocoa - economic analysis - cote d'ivoire - sustainable development
Phase diagram for a mixture of colloids and polymers with equal size
Tuinier, R. ; Smith, P.A. ; Poon, W.C.K. ; Egelhaaf, S.U. ; Aarts, D.G.A.L. ; Lekkerkerker, H.N.W. ; Fleer, G.J. - \ 2008
Europhysics Letters 82 (2008). - ISSN 0295-5075
volume-restriction - behavior - spheres - dispersions - suspensions - cyclohexane - separations - mechanism - chains - latex
We present the phase diagram of a colloid-polymer mixture in which the radius a of the colloidal spheres is approximately the same as the radius R of a polymer coil (q=R/a1). A three-phase coexistence region is experimentally observed, previously only reported for colloid-polymer mixtures with smaller polymer chains (q0.6). A recently developed generalized free-volume theory (GFVT) for mixtures of hard spheres and non-adsorbing excluded-volume polymer chains gives a quantitative description of the phase diagram. Monte Carlo simulations also agree well with experiment
Understanding institutional arrangements: Fresh Fruit and Vegetable value chains in East Africa
Eaton, D.J.F. ; Meijerink, G.W. ; Bijman, J. - \ 2008
Wageningen : Wageningen International (Markets, chains and sustainable development [11]) - ISBN 9789085852285 - 79
economische ontwikkeling - kettingen - fruitteelt - groenteteelt - oost-afrika - landbouwsector - ketenmanagement - institutionele economie - economic development - chains - fruit growing - vegetable growing - east africa - agricultural sector - supply chain management - institutional economics
Thai Dutch Partnership on safe fruit and vegetable supply chains
Stallen, M.P.K. ; Aalberts, C.H.J. - \ 2007
LEI
groenten - vruchten - aanbod - kettingen - thailand - voedselveiligheid - vegetables - fruits - supply - chains - food safety
Pamphlet about Thai Dutch Partnership on safe fruit and vegetable supply chains
A simple relation for the concentration dependence of osmotic pressure and depletion thickness in polymer solutions
Fleer, G.J. ; Skvortsov, A.M. ; Tuinier, R. - \ 2007
Macromolecular Theory and Simulations 16 (2007)5. - ISSN 1022-1344 - p. 531 - 540.
mean-field - chains - polystyrene - potentials - simulation - mixtures - equation - solvent - dilute - phase
We propose simple expressions II/IIo = 1 + and (omega/omega(ex))(3 alpha-1) and (delta(0)/delta)(2) = 1 + (omega/omega(ex))(2 alpha) for the osmotic pressure II and the depletion thickness 6 as a function of the polymer concentration omega. Here, IIo and delta 0 correspond to the dilute limit, and omega(ex) is an extrapolation concentration which is of the order of the overlap concentration omega(ov). The De Gennes exponent a describes the concentration dependence of the semidilute correlation length xi similar to omega(-alpha) it is related to the Flory exponent nu through alpha = nu/(3 nu - 1.). The quantity omega(ex) is experimentally accessible by extrapolating the semidilute limit towards II = IIo or delta = delta(o). These expressions are exact in mean field, where the ratio omega(ex)/omega(ov) (0.49 for II, 0.41 for delta) follows from established models. For excluded-volume chains they describe simulation data excellently: in this case omega(ex)/omega(ov) is 0.69 for II and again 0.41 for delta. We find also very good agreement with experimental data.
Production chains as configurations for development : perspectives for innovation, market development and collaboration
Vellema, S. - \ 2006
Wageningen : Wageningen International (Internationa development discussion paper 2006-1) - 8
landbouwproductie - voedselproductie - kettingen - innovaties - markten - ontwikkeling - agricultural production - food production - chains - innovations - markets - development
Seeing chains for agricultural and food products as a possible instrument for development processes in the South opens up an important discussion about the institutional architecture of agricultural development. One of the major reasons for introducing marketled development schemes has been the growing pressure for downsizing government and public institutions over the past few decades. As a result, supply chains, entrepreneurs and networks between public and private parties have become more and more actively involved in development processes. At the same time, we have seen the international food trade being subjected to increasingly stringent standards by both public legislation and private demands. The fear that these kinds of regulations could exclude large groups of producers has given rise to a debate about the real implications of trade relations and chain formation. It also raises the question of how producers in the South can equip themselves to be in a strong position to take part in international trade and in international chains. It therefore seems important to reflect on the question of what sort of configuration chains really are, and what the options are for reconfiguring them. This article outlines a number of considerations
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